BIOCATALYTIC SYNTHESIS OF POLYMERS .3. FORMATION OF A HIGH-MOLECULAR-WEIGHT POLYESTER THROUGH LIMITATION OF HYDROLYSIS BY ENZYME-BOUND WATER AND THROUGH EQUILIBRIUM CONTROL
Em. Brazwell et al., BIOCATALYTIC SYNTHESIS OF POLYMERS .3. FORMATION OF A HIGH-MOLECULAR-WEIGHT POLYESTER THROUGH LIMITATION OF HYDROLYSIS BY ENZYME-BOUND WATER AND THROUGH EQUILIBRIUM CONTROL, Journal of polymer science. Part A, Polymer chemistry, 33(1), 1995, pp. 89-95
Enzyme-catalyzed preparation of polymers offers several potentially va
luable advantages over the usual polymerization procedures and has bee
n studied for several years. A significant limitation on the polyester
s prepared to date has been the low molecular weights achieved. The pr
esent studies have established that, in the polycondensation of bis(2,
2,2-trifluoroethyl) glutarate with 1,4-butanediol using porcine pancre
atic lipase as the catalyst, this limitation arises from at least two
sources: hydrolysis of activated ester and groups by water introduced
along with the enzyme and the polymerization's reaching equilibrium de
spite using the poorly nucleophilic 2,2,2-trifluoroethanol as the leav
ing group. Evidence is also developed that the presence of trifluoroet
hanol accelerates the release of the enzyme-bound water which hydrolyz
es the activated ester end groups. The hydrolysis could be avoided by
choosing a relatively high-boiling solvent, such as bis(2-ethoxyethyl)
ether, then removing the trifluoroethanol by placing the reaction mix
ture under vacuum periodically or by drying the enzyme rigorously. The
vacuum method also removed the limitation on molecular weight resulti
ng from the reaction's reaching equilibrium. A further improvement in
the molecular weight to nearly 40,000 daltons, well within the range t
hat is technically interesting, was achieved by using 1,2-dimethoxyben
zene or 1,3-dimethoxybenzene as the polymerization solvent. (C) 1995 J
ohn Wiley & Sons, Inc.